Process for the manufacture of rayon paper or non-woven fabric by the wet system



United States Patent PROCESS FOR THE MANUFACTURE OF RAYON PAPER 0R NON-WOVEN FABRIC BY THE WET SYSTEM Yoshikazu Aolri, Otsu, Shiga Prefecture, Teruji Kamei, Sakyo-ku, Kyoto, and Akira Hayami, Kita-ku, Kyoto, Japan, assignors to Tachikawa Research Institute, Higashiyama-lru, Kyoto, Japan, a corporation of Japan No Drawing. Filed May 28, 1963, Ser. No. 283,686

Claims priority, application Japan, May 31, 1962, 37/221,695 5 Claims. (Cl. 162-157) This invention relates to a process for manufacturing a non-woven rayon paper fabric. According to the invention the process combines rayon making with that of paper making. Using incompletely regenerated filaments with high primary swelling value the bonding power between adjacent filaments as prepared by the viscose process is sufiicient to hold the filaments together to form a paper sheet of non-woven fabric after the filaments have been cut and dispersed in water.

Heretofore, rayon paper has been manufactured from short length fibers by conventional paper making machines. However, the regenerated filaments have had no inherent bonding power so that the paper-making could be performed without additives. Even if the fiber beating process is employed, the resulting fibrillation is different from that of natural cellulose fibers and the bonding power resulting from the hydration of cellulose as in the present case is not to be expected. Accordingly, in conventional processes binders are used in amounts from to 30% of the fibers in dispersed solution. The addition of binders such as synthetic high polymers has disadvantages both in terms of cost of production and efiiciency of operation. The need for a commercial process for making rayon paper without binders is thus apparent.

In the present invention, the viscose is extruded into an acid spinning 'bath, and the incompletely regenerated filaments having a primary swelling value of 250% to 2,400% and a residual gamma-value of from 2 to 20 are prepared in stable state, and such spun filaments are cut and dispersed in Water. We have discovered'that the sheet obtained from these swollen filaments has high wet tenacity due to their self-bonding power without the need for binders. Afterwashing and drying, a rayon paper or non-woven fabric having good physical properties'can be obtained. v

According to the present invention incompletely regenerated filaments whose primary swelling value is 250% to 1,900% and whose residual gamma-value is 2. to 20 just afterthe spinning are obtained by suitable selections of the degree of polymerization (DR) of the viscose, its gamma-value and the composition of the spinning bath with particular regard to the sulphuric acid and zinc sulfate contents thereof. The process contemplates a 450 to 900 DP. and a gamma-value of 60 to 100 which is extruded into a spinning bath which contains sulphuric acid of less than 25 g./l., zinc sulfate of less than 2.0 g./l. and sodium sulfate of less than 250 g./l. And then the filaments emerging from the spinning bath are stretched. In this manner, most of the spinning liquor is quickly separated from the filaments and the decomposition of 3,320,117 Patented Maylfi, 1967 "ice the incompletely regenerated filaments ceases. Therefore, these filaments can keep their high gamma-value and are in an alkaline state. Consequently, they are still in fairly stable state.

ample, filaments having a DR of 300 swelling value of 1,500%, persing them in water and they can scarcely be shapedinto paper on account of their bad drainage. But on the other hand filaments having a D1. of 700and a primary swelling value'of 2,200% are easily used for paper-making and a strong rayon paper can be obtained.

The primary swelling value of the incompletely regerierated filaments has a proportional relation to their gamma-value when the filaments are produced from the same viscose and when they are dispersed in water immediately after spinning.

We have found that the lower the sulphuric acid concentration in the spinning bath is the higher the Zinc sulfate concentration, the higher is the primary swelling value of the freshly regenerated filaments. For example, when the viscose having a DR of 760 is spun in a spinning bath under various conditions, the following relationship was found:

The primary swelling value of the filaments increases during settling in water and reaches a maximum (sometimes up to 2,400%) after a few hours settling and then decreases slowly. But. the gamma-value always decreases with the lapse of time; The change of primary swelling value with lapse of time depends especially upon the zinc sulfate content inthe spinning bath, i.e., upon the quantity and quality of zinc Xanthate formed on the surface of the filaments.

The changes of the primary swelling value and the gamma-value while the filaments are in air or water depend principally upon the temperature of the air or water.

When the temperature is low, the changes are very slow.

Accordingly, we can selectively obtain the incompletely regenerated filaments having the primary swelling value within the range of 250% to 2,400% when the spun filaments are cut into desired length of 2 mm. to 20 mm. and subject them to the conventional paper making process, using one of the following conditions: (1) The filaments are dispersed in water'immediately after spinning. (2) The filaments are dispersed in water immediately after spinning in which they remain for several hours. (3) After several hours in air after spinning, the filaments are dispersed in water. (4) After several hours in air after spinning, the filaments are dispersed in water for several hours.

Filaments having a primary swelling value from 250% to 2,400% are easily dispersed in water and give a stable suspension for a long period, and good desirable drainage through the fine wire net of a screen in a paper making machine. When the primary swelling value is below 250%, the tenacity of paper produced is very low, even if sheet formation is possible. In case the value is over 2,400%, the dispersed filaments are apt to swell so much in water that it is impossible to make a smooth wet sheet, because of the slow drainage through the wire net screen.

According to the present invention, by shortening the distance between the adjacent swollen fibers, adequate bonding of each fiber occurs and a strong paper in wet state is produced.

After transference from the wire net, the wire paper sheet is pressed at a desired ratio in order to secure more adhesion of the fibers which are then subjected to an aftertreatment which includes desulphurizing, bleaching or resin finishing, and possibly a softening treatment such as by an alkali-treatment or by furrowing to obtain a softer product.

The characteristics of the present invention are shown as follows: (1) Rayon paper or non-woven fabric is economically produced. (2) The products have superior physical properties, especially breaking length and tear strength in wet state. (3) The products have various properties which are obtained by regulating the primary swelling value, D.P. of cellulose and press ratio, etc. (4) The equipment is simplified because a heater is unnecessary when the wet paper making system is applied.

Examples and properties of the products by the present invention are as follows:

Example 1 Viscose containing 8% cellulose and 5% alkali is prepared from rayon pulp by the usual process for producing conventional viscose rayon. The viscose with a DP. of 300, having 35 sec. of viscosity by falling-ball method and a 45 gamma-value is spun after being ripened at 15 C. for 24 hrs. The spinning bath comprises 25 g./l. sulphuric acid, g./l. zinc sulfate and 310 g./l. sodium sulfate and its temperature is raised to 45 C. The filaments which are extruded through the spinneret with 3,000 holes are stretched to 50% after leaving the spinning bath with a speed of 50 m./min. In this case, the filaments with a primary swelling value of 280% are cut immediately to 6 mm. length, dispersed in water and shaped into paper which are pressed to 3.5 times of dry weight and subjected to the process of refining and drying. The properties of the samples in each example will be summarized in the table found below.

Example 2 Viscose with high DP. and high gamma-value is prepared and spun at 8 hrs. after dissolving. Viscose with DR 540, containing 5% cellulose and 2.8% alkali, having 340 sec. of viscosity and a gamma-value of 68 is spun in the spinning bath comprises 17 g./l. sulphuric acid, 0.5 g./l. zinc sulfate and 40 g./l. sodium sulfate with a temperature of C. The filaments spun from the spinneret with 10,000 holes are stretched to 150% at spinning speed of 15 m./ min. The filaments having the primary swelling value of 520% are cut to 10 mm. length, dispersed in water, formed into paper at press ratio of 3.0 times. The wet paper is treated with hot acid (sulphuric acid 3 g./l., 90 C.), desulphurized by caustic soda of 5 g./l. at 85 C., washed, bleached with 0.1% of available chlorine at C., washed and dried.

Example 3 Viscose with high D.P., high viscosity and high gammavalue is prepared and spun. Viscose with DR 650, containing 4.9% cellulose and 3.0% alkali and having 520 sec. of viscosity with 75 of gamma-value is spun in the spinning bath comprising 22 g./l. sulphuric acid, 2 g./l. zinc sulfate and 200 g./l. sodium sulfate at 37 C. The filaments spun from the spinneret with 10,000 holes are stretched to 180%, giving a primary swelling value of 350%. They are then made into paper following an after-treatment as explained in the above example.

Example 4 The viscose with the DR 760, containing 4.0% cellulose and 3.0% alkali, having 700 sec. of viscosity and 95 of gamma-value is spun in a spinning bath comprising 7.0 g./l. sulphuric acid, 0.8 g./l. zinc sulfate and 60 g./l sodium sulfate at 32 C., and then the filaments are led out of the spinning bath and stretched to 220%. These incompletely regenerated filaments have a primary swelling value of 1,700% and the gamma-value of 18.

Rayon paper is then produced by the wet process with the filaments being cut into .5 or 6 mm., dispersed in water and allowed to settle for 4 hours. At that time the primary swelling value reaches 2,100% and gamma value decreases to 12. This wet sheet of rayon paper is desulphurized, bleached, washed and dried continuously. The rayon paper thus obtained has the properties of parchment paper.

Example 5 Viscose with DR of 600, containing 5.0% cellulose and 4.0% alkali, having 600 sec. of viscosity and of gamma-value is spun into a spinning bath comprising 10 g./l. sulphuric acid, 0.5 g./l. zinc sulfate and 50 g./l. sodium sulfate at 26 C., and the filaments are led out of the spinning bath and stretched to 210%. These incompletely regenerated filaments have the primary swellting value of 1,400% and gamma-value of 15.

Rayon paper is produced by a wet process with the filaments being cut into 6 or 7 mm., dispersed in water and allowed to settle for 4 hrs. At that time the primary swelling value is 950% and the gamma-value is 8. The rayon paper after being formed has a high wet tenacity and permeability. This rayon paper is suitable as a wrapping paper for after-treatment of rayon-cake.

Example 6 The filaments of Example 5 are mixed with crimped staple fibers of 5 or 6 mm. length in one to one ratio. Any synthetic fiber-e.g. polypropylene fibers, nylon fibers, or cotton can be used instead of crimped fibers. These mixtures are shaped into a very soft non-woven fabric by Wet system without binders.

Example 7 The viscose with D.P. 800, containing 4.5% cellulose and 3.5% alkali, having 750 sec. of viscosity and 75 of gamma-value is spun in the spinning bath comprising 15 g./l. sulphuric acid, 0.2 g./l. zinc sulfate and 45 g./I. sodium sulfate at 37 C. And then the filaments are led out of the bath and stretched into 200%.

The incompletely regenerated filaments having a primary swelling value of 670% and a gamma-value of 6 are shaped into a non-woven fabric by the wet process after being in air for 3 hrs. at a temperature of 20 C., and are cut into 6 mm. length and dispersed in water of 15 C. for 1 hr. At that time the primary swelling value changes into 460% and gamma-value decreases at 3. This product is very soft and has high tenacity.

The following table shows that rayon papers manufactured by the present invention are much superior in physical properties especially in wet breaking strength and wet bursting strength compared to those made by conventional method using binders.

TABLE OF MECHANICAL CHARACTERISTICS OF RAYON PAPERS Breaking Length Bursting Factor Tear Factor Exp. Substance Thickness (kn1.) Water Perme- No. D.P. (g./m. (mm.) ability.

(llcmfl/min.) Dry Wet Dry Wet Dry W et 53 0. 13 4. 2. 5. 6 180 48 O. 12 6. 1 3. 4 6.9 180 18 0. 04 5. 1 3.0 9. 1 140 40 0. 4. 5 2.8 4. 8 120 0. 03 5. 1 3. 0 6. 8 140 51 0. 12 3.0 2. 1 3. 5 140 27 Ov 05 6. 5 3. 8 8. 0 210 90 0.35 3.0 0.2 1.8 200 13 0. 04 4. 4 2. 3 3. 8 85 NOTE:

1 8 is a conventional rayon paper produced by wet system with binders. 2 9 is a conventional wrapping paper for after treatment of rayon-cake produced with Manila hemp and by a special treatment for improving wet strength.

cation is calculated by the following equation:

WD X 100 where W is the weight of sample beign centrifuged for 3 min. by the force of 1,000 G after steeping in distilled water at C. for 5 min., and W is the weight of bonedried sample.

What is claimed is:

1. A process for manufacturing rayon paper or other nonwoven fabric by the wet system consisting essentially of the steps of introducing by means of a spinneret viscose having a DR of more than 400 into a single coagulating bath containing from 5 to 30 grams per liter sulphuric acid and from 0.1 to 2.0 grams per liter zinc sulphate, drawing from said single coagulating bath incompletely regenerated cellulosic filaments the residual gamma value of which is from 2 to 20, cutting said incompletely regenerated filaments and dispersing them in water and forming sheets by a conventional paper making process.

2. A process of manufacture as defined in claim 1 wherein said spinning bath contains from 30 grams per liter to 300 grams per liter sodium sulphate.

3. A process of manufacture as defined in claim 1 wherein the temperature of said spinning bath is in the range of from 10 C. to 45 C.

4. A process of manufacture as defined in claim 1 wherein the incompletely regenerated filaments having a swelling value of at least 800%.

5. A process of manufacturing rayon paper consisting essentially of the steps of introducing viscose into a single coagulating bath of low salt content by means of a spinneret, drawing from said single coagulating bath partially regenerated fiber having a residual gamma value cutting said fiber, and making the paper by a conventional paper making process.

References Cited by the Examiner UNITED STATES PATENTS 3,052,593 9/1962 Battista 162157 X 3,114,747 12/1963 Campbell 162157 X 3,139,467 6/1964 Drisch.

3,156,605 11/1964 Anderer 162157 X 3,173,830 3/1965 Wise 162157 X OTHER REFERENCES Hearle: The New Rayons, from Man-Made Textiles, September 1960, pp. 42 to 47.

DONALL H. SYLVESTER, Primary Examiner.

HOWARD CAINE, Examiner. 

1. A PROCESS FOR MANUFACTURING RAYON PAPER OF OTHER NON-WOVEN FABRIC BY THE WET SYSTEM CONSISTING ESSENTIALLY OF THE STEPS OF INTRODUCING BY MEANS OF A SPINNERET VISCOSE HAVING A D.P. OF MORE THAN 400 INTO A SINGLE COAGULATING BATH CONTAINING FROM 5 TO 30 GRAMS PER LITER SULPHURIC ACID AND FROM 0.1 TO 2.0 GRAMS PER LITER ZINC SULPHATE, DRAWING FROM SAID SINGLE COAGULATING BATH INCOMPLETELY REGENERATED CELLULOSIC FILAMENTS THE RESIDUAL GAMMA VALUE OF WHICH IS FROM 2 TO 20, CUTTING SAID INCOMPLETELY REGENERATED FILAMENTS AND DISPERSING THEM IN WATER AND FORMING SHEETS BY A CONVENTIONAL PAPER MAKING PROCESS. 